Rotation servo circuit in disk player

Abstract: The rotation servo circuit consists of a rough servo circuit (60) and a phase lock servo circuit (70), wherein first the rough servo circuit (60) functions to pull the phase approximately into its precision range, and then the rough servo circuit (60) is switched by means of a changeover switch (27) to the phase lock servo circuit (70) which performs a high-precision control action. When the rough servo circuit (60) is switched over to the phase lock servo circuit (70) in a seek operation, the gain Gp of an amplifier (73) in the speed loop of the phase lock servo circuit (70) is set to - ∞, so that the phase lock servo circuit functions as a primary-loop structure merely with the speed loop.

Description: BACKGROUND OF THE INVENTION The present invention relates to a rotation servo circuit in a disk player for reproducing recorded audio data from a digital audio disk such as CD (Compact Disc) or MD (Mini Disc) and also from a data recording disk (hereinafter simply referred to as a disk) inclusive of CD-ROM. The spindle (rotation) servo system adopted in the known disk players has a rotation servo circuit which comprises a rough servo system for pulling the disk rotation speed approximately into a desired precision range and a phase lock servo system for attaining a higher precision after the control action of the rough servo system. This phase lock servo system has a secondary loop structure which consists of a phase loop for executing a phase locking control in accordance with the phase difference between a reproduced sync signal and a reference sync signal, and a speed loop for measuring the period of a reproduced frame sync signal obtained from the disk and equalizing the frequency thereof to a reference frequency of 7.35 kHz. Meanwhile the rough servo system has a primary loop structure which extracts the lowest-frequency component of the reproduced signal and equalizes the frequency of the extracted component to the reference frequency. In the control action of the rotation servo circuit, first the disk rotation speed is pulled approximately into the desired precision range by the rough servo system. As a result, the phase-locked loop (PLL) of the phase lock servo system is locked to attain a state where data is reproducible from the disk. When the PLL is thus locked, the primary-loop rough servo system is switched to the secondary-loop phase lock servo system. However, in the conventional rotation servo circuit of the above-described construction, there arises a problem that a phase-locked state is not held at the moment the rough servo system is switched over to the phase lock servo system, although the disk rotation speed is substantially kept stable. And in an exemplary case where the frame jitter margin is set to ±27 frames and the existing deviation is a maximum of 27 frames, it follows that such state is forcibly pulled into synchronism to consequently cause a disorder in the rotation speed at this moment, whereby the PLL is induced to be out of phase. If the PLL is rendered out of phase in this manner, it is impossible to read each subcode recorded as an index for the data on a disk. Therefore, an operation of reading the subcode becomes possible posterior to the lapse of a fixed time which is required until the disk rotation speed is stabilized after the rough servo system is switched to the phase lock servo system. In a seek operation for relocating an optical pickup to a desired address position (target address position) on a disk, as shown in Fig. 1, there are performed a series of operations of first switching the phase lock servo system to the rough servo system, then replacing the pickup in the radial direction of the disk by a distance corresponding to a required number of tracks, subsequently switching the rough servo system to the phase lock servo system after the disk rotation speed has reached, approximately, its regular linear velocity, and reading the subcode from the disk. The above operations are repeated until the pickup has arrived at the target address position. Therefore, if the disk rotation speed is disordered at the moment of switching the rough servo system to the phase lock servo system as described, a speed disorder is caused at each time of the repeated operations of switching from the rough servo system to the phase lock servo system during the seek, whereby the time required for reading out the subcode is prolonged to eventually fail in shortening the seek time. Particularly in reproduction of data from a CD-ROM or the like where a fast seek is necessary, any disorder of the disk rotation speed causes a waste of time in reading out the subcode, hence raising an important problem in realizing fast seek. OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide a rotation servo circuit for use in a disk player where a subcode can be read from a disk at the time of switching from a rough servo system to a phase lock servo system to thereby attain a great reduction of a seek time. To achieve the above object, the present invention provides a rotation servo circuit for use in a disk player having a first servo circuit for detecting the speed difference between the rotation speed of a disk and a reference speed thereof and then controlling the rotation of the disk in accordance with the detected speed difference, and a second servo circuit of a secondary loop structure which consists of a phase loop for detecting the phase difference between a reproduced sync signal obtained from the disk and a reference sync signal and then controlling the rotation of the disk in accordance with the detected phase difference. The rotation servo circuit further comprises a speed loop for measuring the period of the reproduced sync signal and controlling the rotation of the disk on the basis of the measured period, wherein the rotation control by the second servo circuit is executed posterior to completion of the rotation control by the first servo circuit. At the time of reading the recorded data from the disk by an optical pickup, both the phase loop and the speed loop are closed to execute the rotation control. At the time of a seek, the optical pickup is displaced in the radial direction of the disk in a state where the second servo circuit is turned off while the first servo circuit is turned on, and after a certain displacement of the optical pickup corresponding to a predetermined number of tracks, the position data are read from the disk in a state where the first servo circuit is turned off while only the speed loop of the second servo circuit is closed, and a series of such operations are repeatedly executed until arrival of the optical pickup at its desired target position. In the disk player of the above construction, a disk is played while being rotated at a higher speed (e.g., 4-fold speed) than a normal or regular speed, and the data reproduced from the disk are stored in a bulk memory of a large capacity, while the stored data are read out successively from the memory at a normal output data rate. The data quantity stored in the bulk memory is continuously monitored, and the entire servo systems are turned off when the memory has become full of the data. In such off-state, the stored data in the bulk memory are successively read and outputted therefrom. When the bulk memory has become substantially empty, the entire servo systems are turned on again, then the optical pickup is displaced back to the final read position corresponding to the preceding turn-off of the servo systems, and the high speed reproduction is resumed from the link point, whereby the on-time period of each servo system is shortened to consequently lower the power consumption. In the rotation servo circuit of the present invention, for use in a shock-proof disk player employing a bulk memory of a large capacity, there may be prepared a high speed mode and a low speed mode for driving a disk, the high speed mode being selected only at the occurrence of a track jump to thereby realize low power consumption in the disk player. Also in this rotation servo circuit, two clock signals of mutually different frequencies corresponding to the two driving modes are prepared as reference clock signals for speed control, and one of such clock signals of different frequencies is adequately selected to switch the driving mode. Since the structural requisite is merely to switch the frequency of the reference clock signal, the circuit configuration can be simplified to consequently lower the production cost of the disk player. Further the rotation servo circuit of the invention may be contrived in such a manner that, at the time of switching from a rough servo system to a phase lock servo system in a seek, only the speed loop of the phase lock servo system is closed so that the phase lock servo system functions as a primary loop. At the time of switching the servo system, the phase of the reproduced sync signal is somewhat disordered, but none of forcible phase pull-in action is executed, whereby the rotation speed of the disk is kept stable. If the disk rotation speed is thus stable, the operation of reading out a subcode can be performed without any problem even when some disorder of the phase is existent. Accordingly it becomes possible to read out the subcode immediately after switching the servo system, hence eliminating the waste of time for reading out the subcode to eventually shorten the required seek time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory diagram illustrating a seek operation in the related art; Fig. 2 is a block diagram of an embodiment of the present invention applied to a CD player, Fig. 3 is a block diagram of a rotation servo circuit portion of a CD player corresponding to an embodiment of the present invention; Fig. 4 is an explanatory diagram illustrating a seek operation performed in the CD player of Fig. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter some preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 2 is a block diagram showing an embodiment of the present invention applied to, e.g., a CD player. In this diagram, a disk (CD) 1 is driven by a spindle motor 2, and recorded data are read from the disk 1 by an optical pickup (hereinafter referred to simply as pickup) 3. It is assumed in this embodiment that the disk 1 is rotated at a 4-fold speed higher than a normal regular speed in an ordinary CD player. The pickup 3 comprises a laser diode 4; an objective lens 5 for converging a laser beam, which is emitted from the laser diode 4, to form a data-reading light spot on the signal plane of the disk 1; a polarized beam splitter 6 for changing the travel direction of the laser beam reflected from the disk 1; and a photo detector 7 for receiving the reflected laser beam. The pickup 3 is displaceable in the radial direction of the disk by a driving source such as a sled feed motor (not shown). The pickup 3 further comprises, although not shown, a tracking actuator for displacing the data-reading light spot to a record track on the disk 1 in the radial direction of the disk, and a focus actuator for moving the objective lens 5 along its optical axis. The output signal of the pickup 3 is supplied to an I-V (current-voltage) amplifier 8 where the current signal is converted into a voltage signal, which is waveform-shaped in an RF equalizer 9 and then is supplied to a DSP (digital signal processor) 10. Now a description will be given on how the signal is processed in the DSP 10. First in a PLL asymmetry corrector 11, a binary signal is obtained with execution of asymmetry correction, and successive clock pulses are generated by a PLL (phase-locked loop) structure in synchronism with the edge of the binary signal. Here, "asymmetry" signifies a state where the center of the eye pattern of the RF signal deviates from the center of the amplitude. Subsequently, EFM (eight-to-fourteen modulation) data are demodulated in an EFM demodulator 12, whereby digital audio data and an error correction-detection parity code are obtained, and simultaneously the subcode recorded immediately after the frame sync signal is also demodulated. The subcode thus demodulated in the EFM demodulator 12 is supplied via a subcode processor 13 to an undermentioned controller 20. The data after the EFM demodulation are once stored in a RAM 14, and error correction is executed in an error corrector 15 on the basis of the error correction-detection parity code. Then the error-corrected data are deinterleaved in a deinterleaver 16 so that the data are decoded from CIRC (cross interleave Reed-Solomon code). The data processed in the DSP 10 are once stored in a bulk RAM 23 of a large capacity via a RAM control signal processor 22. The data thus stored in the bulk RAM 23 are read out therefrom via the RAM control signal processor 22 at a data rate equal to 1/4 of the rate for data reproduction from the disk 1, i.e., at the normal output data rate in an ordinary CD player. And after being filtered through a digital filter 24, the data are converted into analog data in a D-A converter 25 and then are delivered as audio outputs of left (L) and right (R) channels. The bulk RAM 23 is used for preventing a sound skip by maintaining the continuity of the reproduced audio data when any track jump has occurred during a reproduction mode due to some external disturbance such as shock. Occurrence of a track jump is detected by continuously monitoring the subcode in the controller 20 and recognizing the discontinuity of a time code included in the subcode. More specifically, upon occurrence of a track jump during data reproduction, the data-reading light spot of the pickup 3 is returned to the position immediately before the track jump, and then the data reproduction is resumed from that position while the audio data reproduced posterior to resumption of the reproduction are linked to the audio data reproduced immediately before occurrence of the track jump and stored in the bulk memory 23. The ratio between the data writing rate in the bulk RAM 23 and the data reading rate therefrom is 4:1, i.e., the data are written at a 4-fold higher speed in comparison with the data reading speed, so that there soon occurs an overflow of the data in the bulk RAM 23. It is therefore necessary to continuously monitor the data quantity stored in the bulk RAM 23. The operation of monitoring the data quantity in the bulk RAM 23 is performed in the RAM control signal processor 22. More specifically, the RAM control signal processor 22 recognizes the last address of the data written in the bulk RAM 23 as a definite address, and also recognizes the address of the read data as an address 0. And when the data quantity in the bulk RAM 23 has exceeded a first preset value, the RAM control signal processor 22 determines an overflow of the bulk RAM 23 on the basis of the definite address and outputs an overflow signal (first control signal). Meanwhile, when the data quantity has become smaller than a second preset value which is lower than the first preset value, the RAM control signal processor 22 determines that the bulk RAM 23 is approximately empty, and then outputs an empty signal (second control signal). Thus, the signal processor 22 functions as a memory control means. The RAM control signal processor 22 continuously feeds the recognized definite address to the controller 20 while supplying thereto an overflow signal or an empty signal. The controller 20 consists of a CPU and recognizes the definite address, 5 which is obtained from the RAM control signal processor 22, as a definite subcode in correspondence to the subcode. The controller 20 further functions as a servo control means which, on the basis of the overflow signal/empty signal supplied from the RAM control signal processor 22, executes on/off control of a spindle servo signal processor (first servo means) 18 for controlling the rotation speed of the spindle motor 2, and also on/off control of an optical-unit servo signal processor (second servo means) 26 for controlling the tracking, focus and sled servo system relative to the operation of the pickup 3. More specifically, the controller 20 turns off the spindle servo signal processor 18 and the optical-unit servo signal processor 26 in response to an overflow signal outputted from the RAM control signal processor 22, or turns on the spindle servo signal processor 18 and the optical-unit servo signal processor 26 in response to an empty signal outputted from the RAM control signal processor 22. The DSP 10 includes a spindle servo signal processor (rotation servo circuit) 18 for controlling the rotation of the spindle motor 2 on the basis of the phase difference between a reproduced clock signal and a reference clock signal. The optical-unit servo signal processor 26 functions to control the individual servo systems relative to the operations of the pickup 3, i.e., the tracking servo system for enabling the data-reading light spot to follow the record track on the disk 1, the focus servo system for continuously focusing the light spot on the signal plane of the disk 1, and the sled servo system for controlling the position of the pickup 3 in the radial direction of the disk. Fig. 3 is a block diagram of the spindle servo signal processor (rotation servo circuit) 18 of the invention. As shown in this diagram, the spindle servo signal processor 18 according to the invention comprises a rough servo circuit (first servo circuit) 60 for pulling the rotation speed of the disk 1 approximately into its precision range, and a phase lock servo circuit (second servo circuit) 70 for executing a high-precision control action after the operation of the rough servo circuit 60. In the rough servo circuit 60, a period measurer 61 functions to measure the period of a frame-sync corresponding portion in an EFM signal reproduced from the disk 1, thereby detecting the minimum frequency signal 11T (T : fundamental unit length of pit) on the disk 1. The signal 11T thus obtained is passed through a peak hold circuit 62 and a bottom hold circuit 63, so that any signal component greater than 11T and generated due to some flaw or the like is screened, whereby the original reproduced frame sync signal is detected. The reproduced frame sync signal is multiplied by G in an amplifier 64 and then is supplied via a changeover switch 27 to a spindle drive 28. The rotation speed of the spindle motor 2 is so controlled that the period of the reproduced frame sync signal is equalized to the reference time length of 2.544 µsec (≈ 11/4.3218 x 10 6 ). As for the rough servo circuit 60, the construction disclosed in, e.g., Japanese Patent Publication No. Hei 1 (1989)-35419 may be used as well. Meanwhile the phase lock servo circuit 70 is formed into a secondary loop structure which consists of a phase loop for executing a phase locking control in accordance with the phase difference detected by a phase comparator 71 between a reference clock signal RFCK and a reproduced clock signal WFCK of a period ranging from one reproduced frame sync signal to another reproduced frame sync signal, and a speed loop for measuring the period of the reproduced clock signal WFCK by means of a period measurer 72 and controlling the measured period in such a manner as to equalize the frequency thereof to a reference frequency of 7.35 kHz. As for the phase lock servo circuit 70, the construction disclosed in, e.g., Japanese Patent Laid-open No. Hei 2 (1990)-101676 may be used as well. In the phase lock servo circuit 70, the output of the phase comparator 71 is multiplied by G P in an amplifier 73, while the output of the period measurer 72 is multiplied by G S in an amplifier 74. The respective outputs of the two amplifiers 73 and 74 are added to each other in an adder 75, whose output is then supplied via the changeover switch 27 to the spindle drive 28, whereby the aforementioned control action is executed. The operation of switching the servo systems in the spindle servo signal processor 18 is performed by actuating the changeover switch 27 in response to a servo switching signal outputted from the controller 20 (see Fig. 2). More specifically, first the switch 27 is changed to turn on the rough servo circuit 60, which then pulls the disk rotation speed approximately into its precision range to thereby lock the PLL in the phase lock servo circuit 70, so that reproduction of the data from the disk 1 is rendered possible. Immediately after the PLL is locked, the switch 2 is changed again to turn on the phase lock servo circuit 70 while turning off the rough servo circuit 60, whereby the primary-loop rough servo system is switched to the secondary-loop phase lock servo system. In a seek mode, as described before, the pickup 3 is displaced in the radial direction of the disk 1 after the phase lock servo system is switched to the rough servo system, and when the rotation speed of the disk 1 has reached approximately its predetermined linear velocity with a displacement of the pickup 3 corresponding to a predetermined number of tracks, the phase lock servo system is turned on again and the subcode is read out from the disk 1. Such a series of operations are repeatedly performed until the pickup 3 has arrived at a desired target address position. As the pickup 3 is displaced in the radial direction of the disk 1 in the seek mode, the data-reading light spot traverses the record tracks (pit strings), so that a sinusoidal tracking error signal is generated during the traverse period shown in Fig. 4. And the number of tracks traversed by the data-reading light spot is counted on the basis of such a tracking signal. This embodiment is so contrived that, when the rough servo system is switched to the phase lock servo system at the time of a seek, the gain GP of the amplifier 73 on the phase loop side is set to ∞ in response to a loop on/off signal outputted from the controller 20 (see Fig. 2). Therefore, when the rough servo system is switched to the phase lock servo system in the seek mode, the phase lock servo system functions as a primary loop structure where the phase loop is opened and only the speed loop is closed. In this manner, the phase loop of the phase lock servo system is opened at a transition from rough servo to phase lock servo, so that none of forcible phase pull-in action is executed. Consequently, as shown in Fig. 4, the rotation speed of the disk 1 is not disordered immediately after switching of the servo systems and is kept substantially stable. Thereafter the rotation speed of the disk 1 is controlled merely by the speed loop alone in the primary loop structure. In such a state under control of the phase lock servo system in the primary loop structure, the rotation speed of the disk 1 is maintained stable even if the phase is not locked, whereby no problem is raised in reading out the subcode. As a result, at the time of a seek when the rough servo system and the phase lock servo system are switched alternately and repeatedly, the subcode can be read immediately after such switching, so that any waste of time in reading the subcode is eliminated to consequently realize wide reduction of the required seek time. However, in reproducing PCM audio data, proper deinterleave fails to be performed in the deinterleaver 16 (see Fig. 2) if a phase-locked state is not ensured. Therefore it is necessary in such a case to execute speed control by a secondary loop structure where both of the phase and speed loops are closed in the phase servo lock system. The embodiment mentioned above represents an exemplary case of applying the present invention to a CD player. However, it is to be understood that the present invention is not limited to such an example alone and may be applied to any of other disk players designed for data reproduction from MD, CD-ROM and so forth. Thus, in the rotation servo circuit of the present invention comprising a rough servo system and a phase lock servo system, the rough servo system pulls the phase approximately into its precision range and then is switched to the phase lock servo system which executes high precision control. And when the rough servo system is switched to the phase lock servo system in a seek mode, only the speed loop of the phase lock servo system is closed so that this servo system functions as a primary loop structure. Consequently, although the phase is somewhat disordered at the time of switching the servo system, the disk rotation speed is kept stable and the subcode can be read from the disk, so that any waste of time in reading the subcode is eliminated to eventually achieve remarkable reduction of the required seek time. Accordingly, the rotation servo circuit of the present invention is optimal for a disk player which reproduces data from a CD-ROM or the like where a fast seek is particularly necessary.

Claims: A rotation servo circuit (18) for use in a disk player having a first servo circuit (60) for detecting the speed difference between the rotation speed of a disk (1) and a reference speed thereof and then controlling the rotation of the disk (1) in accordance with the detected speed difference, and a second servo circuit (70) of a secondary loop structure which consists of a phase loop (71, 73) for detecting the phase difference between a reproduced sync signal (WFCK) obtained from the disk (1) and a reference sync signal (RFCK) and then controlling the rotation of the disk in accordance with the detected phase difference, and a speed loop (72, 74) for measuring the period of the reproduced sync signal (WFCK) and controlling the rotation of the disk on the basis of the measured period, wherein the rotation control by said second servo circuit (70) is executed posterior to completion of the rotation control by said first servo circuit (60), and at the time of reading the recorded data from the disk (1) by an optical pickup (3), both of said phase loop and said speed loop are closed to execute the rotation control; wherein, at the time of a seek, said optical pickup (3) is displaced in the radial direction of the disk (1) in a state where said second servo circuit (70) is turned off while said first servo circuit (60) is turned on, and after a certain displacement of said optical pickup (3) corresponding to a predetermined number of tracks, the position data are read from the disk in a state where said first servo circuit (60) is turned off while only the speed loop (72, 74) of said second servo circuit (70) is closed, and a series of such operations are repeatedly executed until arrival of said optical pickup (3) at its desired target position.

Inventors: AKITA MAMORU, SHIMIZUME KAZUTOSHI, AKITA, MAMORU, SHIMIZUME, KAZUTOSHI, AKITA, MAMORU, SONY CORPORATION, Shimizume, Kazutoshi, Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: G11B7
IPC codes: G11B7, G11B19, G11B20, G11B27